Dependence of Bearing Fatigue Life on Film Thickness to Surface Roughness Ratio

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Abstract
A statistical expression, showing as a function of the film parameter (film thickness/surface roughness or h/σ) the fractional reduction in fatigue life at “full film” conditions due to the competition between asperity induced fatigue and fatigue due to indigenous surface defects and subsurface inclusions, is presented. Several sources of endurance test data relating the fatigue life of a rolling bearing to the film parameter are reviewed. To unify the experimental data a “relative” fatigue life raised to the power of e, the Weibull dispersion parameter, is plotted against the film parameter. Comparisons between the theoretical and experimental results are then made which reveal that the increase in bearing fatigue life due to the film parameter can be described by the theoretical model with a “reference” film parameter value of 1.5 for h/σ > 0.5. For h/σ < 0.5, the variation of h/σ explains only a minor portion of the scatter of the fatigue lives.